Engine won't start - Check hybrid system

[nepo]

Hi,

I hope that you can help me with my problem, as my Toyota dealership here in Europe can't help me further. As you guys in the States have more experience with Lexus I hope that you have heard of such a problem allready. Please appologize for my mistakes in english in advance.

I own a Lexus GS450h 2007. Severel weeks ago after a freezing night I wanted to drive to work. The engine started and died after several seconds with the message check hybrid system and a red exclamation mark. There was no yellow check engine sign and the "ready" sign was still on. The engine fans went on. I could drive on electric power. Each time after that point I tried to start the car, the engine died immideately after starting and I wasn't able to drive the car. No ready sign appeared and allways the message check hybrid system with the reg exclamination mark and engine fans on. After that the car was towed to a toyota dealership. The car doenst't have any trouble codes in the ecu and that makes the problem complicated. They can only read the trouble codes after dissconection and connecting the battery. When the computer is attached an they try to start the car the communication between ecu and computer aborts and the message appears as above. They have no possibility to acces the ecu unless they disconnect and reconnect the battery. The dealership tried many things. They checked the sensors, some integration relay, they even tried an other ecu from an other gs450h and there is still this problem. The 12V battery was changed but that didn't help. The HV-battery was changed half a year ago as it was under warranty.

Did anybody have simmilar problems with the check hybrid system message and that the engine doesn't start but no trouble codes in the ecu.

Is there anything on the car that isn't monitored by the ecu.

Any ideas are welcome and thank you very much in advance.